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article i nfo We applied different methods (differential scanning calorimetry, circular dichroism, Fourier transform infrared spectroscopy, and intrinsic fluorescence) to investigate the thermal-induced changes in the structure of small heat shock protein Hsp22. It has been shown that this protein undergoes thermal-induced unfolding that occurs within a very broad temperature range (from 27 °C to 80 °C and above), and this is accompanied by complete disappearance of α-helices, significant decrease in β-sheets content, and by pronounced changes in the intrinsic fluorescence. The results confirm predictions that Hsp22 belongs to the family of intrinsically disordered proteins (IDP) with certain parts of its molecule (presumably, in the α- crystallin domain) retaining folded structure and undergoing reversible thermal unfolding. The results are also discussed in terms of downhill folding scenario. © 2009 Elsevier B.V. All rights reserved.